It is known that polysiloxane-polycarbonate block cocondensates have good properties in relation to low-temperature (notched) impact resistance, chemicals resistance and outdoor weathering resistance, and also good ageing properties and flame retardancy. In terms of these properties they are sometimes superior to conventional polycarbonates (homopolycarbonate based on bisphenol A).
Industrial production of these cocondensates mostly proceeds from the monomers by way of the interfacial process with phosgene. It is moreover known that these siloxane cocondensates can be produced by way of the melt transesterification process with use of diphenyl carbonate. These processes have the disadvantage that the plants used are used for the production of standard polycarbonate, and are therefore large. Production of specialized block cocondensates in these plants is often uneconomic because the volume of the said products is relatively small. The starting materials, e.g. the polydimethylsiloxanes, required for the production of the cocondensates can moreover adversely affect the plant, because they can contaminate the plant or the solvent-circulation systems. The production process moreover requires toxic starting materials such as phosgene or, in the case of the melt transesterification process, has high energy consumption.